Rubbery copolymers containing a majority of isobutylene units are well known for their low gas permeability, unique damping properties, and low surface energy; these properties make such copolymers particularly desired in applications such as tire innerliners. In order to have a better compatibility or co-curability with other elastomer components in the end applications, an unsaturated comonomer and/or a comonomer containing reactive functionality is introduced into the isobutylene rubbery polymer. Previously known comonomers include, for example, isoprene and p-methylstyrene. The copolymer may be partially brominated to give better compatibility.
The tire industry has a desire to enhance the barrier property of elastomers used in inner tubes and innerliners. Elastomer nanocomposites have been developed to satisfy this need. Nanocomposites are polymer systems containing inorganic particles with at least one dimension in the nanometer range. Some examples of these are disclosed in U.S. Pat. Nos. 6,060,549; 6,103,817; 6,034,164; 5,973,053; 5,936,023; 5,883,173; 5,807,629; 5,665,183; 5,576,373; and 5,576,372. Common types of inorganic particles used in nanocomposites are phyllosilicates, an inorganic substance from the general class of so called “nanoclays.” Ideally, intercalation should take place in the nanocomposite, wherein the polymer inserts into the space or gallery between the clay surfaces.
The layered clay can adapt to five different states in the base polymer. The first state is “particle dispersion” wherein the clay particle size is in the order of microns but uniformly dispersed in the base polymer. The terms aggregate and agglomerate have been used to describe this state. The second state is an “intercalated” state wherein polymer chains are inserted into the layered clay structure, this occurring in a crystallographic regular fashion, regardless of the polymer to clay ratio. Intercalated states may typically contain several layers of polymer between organoclay plates. An increase in the gallery spacing of the nanoclay, swollen with rubber, from a pristine state of about 0.3 to 0.7 nm up to about 2.0 to 6.0 nm can be considered as creating an intercalated condition. The third state is a “flocculated” state. This is conceptually the same as intercalated states; however, the individual clay layers are sometimes flocculated or aggregated due to hydroxylated edge to edge interactions of the clay layers. The fourth state is an “intercalated—flocculated” state. The clay plates in this intercalated-flocculated state can be separated; however, tactoids or agglomerates can form that have a thickness in the range of 100 to 500 nm. The fifth state is an “exfoliated” state. In an exfoliated state, the individual clay layers are separated within a continuous polymer by an average distance that depends on the clay concentration or loading in the polymer. It is therefore desirable to have exfoliation, preferably where the polymer is fully dispersed with the individual nanometer-size clay platelets.
It is also desirable to have the desired orientation of the platelets in the formulation to be perpendicular to the flow of gas. This state is particularly desirable as the regular arrangement of the platelets is thought to be effective in blocking the diffusion of gas molecules. Therefore articles containing formulations that present the clay in an exfoliated state and/or with clay platelets in the oriented perpendicular to the flow of gas are desirable. Accordingly, there is a need for formulations that present the clay in the exfoliated state and/or having an orientation perpendicular to the flow of gas, to improve barrier properties.
Additionally, in elastomeric formulations having additives of both carbon black and inorganic clays, the interaction between the polar surface groups of the carbon black and the hydrophilic nanoclays can make it challenging to achieve a good clay dispersion or exfoliation within the elastomer, or desirable orientation of the nanoclay platelets within the elastomer. Accordingly, there is a particular need to reduce the interaction between the nanofillers in elastomeric nanocomposites, to ultimately improve barrier properties.